1-29 Organelles and Protein Sorting Flashcards Preview

MSI Unit I > 1-29 Organelles and Protein Sorting > Flashcards

Flashcards in 1-29 Organelles and Protein Sorting Deck (48):

targeting of newly synthesized enzymes to mitrochondria involves which transport mechanisms?

transmembrane transport


proteins encoded by the mitochondrial genome (synthesized where)? carry out functions in which compartment of the mitrochondria?

synthesized in matrix, transported to inner membrane. they are all components of the ETC or ATP synthase complex (both localized in inner membrane)


the mitochondrial genome encodes

rRNAs, tRNA,s and mRNAs


where is the mito genome located?

in the mito matrix


how many copies of mito genome are in each mitro?

several copies


mito uses a ____________ than the nuclear genome

slightly different genetic code


What is synthesized in the mito?

ATP (atp synthatase), DNA (during replication), RNA (when transcribed into 2 giant strands), Proteins (13 are synthesized within mito)


what is NOT synthesized in mito?

oligosaccharides. they are synthesized in the ER and Golgi


ETC occurs in which compartment?

the inner membrane


proteins are imported into the mito matrix _______



What effect does maternal inheritance of mito genes have on mutation frequency?

no effect.


synthesis of mtDNA encoded proteins occurs in the

mitochondrial matrix


x-linked adrenoleukodystrophy is caused by defects in

the fatty acid transporter in peroxisomal membranes.

a defect leads to a build up of long fatty acids in cytoplasm - toxic- leads to demyelination of neurons.



proteins synthesized in the ER are modified here


worn out organelles are digested in the



where are mitochondria located?

either in areas that need lots of ATP or around the cell along microtubules


structure of mitochondria from outside to inside

Outer membrane, intermembrane space, matrix, inner membrane


Matrix space

large internal space

lots of enzymes for breaking down fatty acids and citric acid cycle

contains mito genome with machinery


inner membrane

encloses matrix

convoluted cristae to increase SA for ETC and ATP synthetase (both necessary for oxid phosp)

Electrochemical gradient that powers ATP syntehsis is established across the membrane by the ETC


outer membrane

separates the mito from cytosol

contains porins across lipid bilayer, permeable to small molecules


intermembrane space

small space between inner/outer membrane

contains cytocrome C component of ETC, also gets released signaling apoptosis


final destination of proteins depends on

amino acid sequences which may contain sorting signals, directing them to an organelle

no sorting signal - stay in cytosol


three mechanisms of protein transport

nuclear pores (GAF/GEF), protein translocators (co-translation or translationally, and vesicles (ER to Golgi to PM/extracellular space/lysosomes


three mechanisms of protein transport

nuclear pores (GAF/GEF)

protein translocators (co-translation or translationally

vesicles (ER to Golgi to PM/extracellular space/lysosomes



signal recognition particle - recognizes the signal sequence, directs it to correct organelle


process of importing proteins to mitochondria

Transport mediated by two protein translocators (TOM & TIM complexes) located in outer and inner membranes

1. Precursor protein binds its recept sequence to receptor on TOM

2. Precursor protein and TOM move laterally across outer membrane until encouters TIM complex

3. Unfolded precursor protein translocates across both membranes, signal sequecne first. Chaperone proteins in matrix help pull the protein across the two membranes

4. Signal sequence cut off by microchondrial signal peptidase - protein unfolds to active confirmation with help for other chaperone proteins


structure of peroxisomes

small multifucntional organelles found in all eukaryotic cells.

Major site of oxygen utilization, contains high concentrations of oxidatize enzymes used in reactions that break down molecules includig toxins, alcohol, and fatty acids, also synthesize special phospholipids.

Cells have hundreds


3 functions of peroxisomes

Oxidative degradation - remove hydrogen atoms from organic substrates to produce hydrogen peroxide. Catalase uses h2o2 to oxidize/detox molecules

Beta oxidation (break down of fatty acids)

Synthesis of cholestrol, bile acids, some lipids - essential for making the plasmologens of myelin sheaths


describe the mitochondrial genome

i. Very small circular ds DNA
ii. 37 genes for 2 rRNAs, 22 tRNAs, and 13 polypeptides
iii. Very little non-coding (junk) sequences
iv. No introns
v. Genetic code varies slightly from nuclear

Each mito contains 10-20 copies of the genome. Each cell therefor has thousands of copies


Mitochondrial replication

a. Replication - occurs throughout cell cycle, on average the total number of mtDNA molecules doubles with each cell cycle


mitochondrial transcription

both strands of mtDNA transcribed from single promoter region on each strand. Produces 2 giant rna molecules, each cleaved to give 2 rnas, 22 trnas, and 13 mRNA's.


mitochondrial translation

occuring in matrix using tRNAs and rRNAS encoded by mito genome. Produces only 13 pp, all of which involved in eT and oxidative phos


basic principles of mito genetics and inheritance

maternal inheritance

heteroplasmy/threshold effect - homoplasmy penetrance can decrease due to environmental factors

mtDNA has high mutation rate


mutation rate of mtDNA?

much higher than normal

-no introns = all mutations are within a coding sequence
-no protective histones
-inefficient repair
-mtDNA is exposed to oxygen free radicals


describe mito disorders

often late onset due to increasing mutations over time. Broad range of tissues but usually those that require most oxidative phosphorylation - neuropathies, myopathies, etc..


release of cytochrome c

triggers a caspase cascade creating lots of proteolytic enzymes that cause apoptosis



uses hydrogen peroxide to oxidize substrates. Important in detoxifying areas of teh body like kidney and liver cells.


synthesis of mtDNA encoded proteins occurs in the..

mitochondrial matrix


What is the role of the mitochondria in the intrinsic pathway of apoptosis?

Releases cytochrome c from the intermembrane space into the cytosol which triggers activation of the caspase cascade


What is the caspase cascade?

Triggered by the release of cytochrome c from the intermembrane of the mitochondria into the cytosol, the caspase cascade is an intracellular proteolytic cascade responsible for cleaving key cellular proteins


What are TOM/TIM and what do they do?

TOM-protein Translocator located in Outer Membrane
TIM-protein Translocator located in Inner Membrane

Precursor protein binds to a receptor associated with TOM (must reach outer membrane first), via signal sequence. This complex will diffuse laterally until they reach TIM...protein is in folded state at this point, then chaperone proteins in the matrix pull protein through two membranes


What do chaperone proteins do?

located in the mito matrix, they pull the protein being translocated through TOM/TIM into the matrix...where the mito signal sequence is cleaved off by mito signal peptidase and protein re-folds into its final conformation


if you destroy the electrochemical gradient across the inner membrane, what happens to protein transport?

It stops.


DNA replication is limited to the S phase in both nuclear DNA and mito DNA replication

False...mito DNA replication occurs throughout cell cycle


Where does translation of mito proteins occur? How many polypeptides are made and where do they go after translation?

Occurs in mito matrix, synthesizes 13 polypeptides that all go to the inner membrane to function in the ETC and oxidative phosphorylation


What is heteroplasmy and the threshold effect?

Heteroplasmy is when mutant and WT mtDNA both express in cells at different percentages...resulting in variable espressivity...differences in severity of disease. A phenotype will not be apparent until a threshold is reached...known as the threshold effect.


What is homoplasmic?

Homoplasmic is when all of a woman's mtDNAs carry a particular mutation...in this case, all of her children will inherit the mutation and any disease associated with with it


What is N-linked glycosylation and where does this occur?

N-linked glycosylation is a protein modification that occurs in the ER. A preformed oligosaccharide (sugar) of 14 sugars is attached to a.a. residues during translocation (co-translationally).

N-linked glycosylation modification begins in the ER, but continues in the golgi

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